1. Field of the Invention
The present invention relates generally to semiconductor manufacturing techniques and methods of forming electrical contacts in semiconductor substrates. More particularly, the present invention relates to methods of forming through-wafer interconnects in semiconductor substrates and structures resulting therefrom.
2. State of the Art
Semiconductor substrates often have vias extending therethrough, wherein the vias are filled with conductive materials to form interconnects (commonly known as a through-wafer interconnect, or “TWI”) used, for example, to connect circuitry on one surface of the semiconductor device to circuitry on another surface thereof, or to accommodate connection with external circuitry.
As used herein, a “via” refers to a hole or aperture having conductive material or a conductive member therein and which extends substantially through a substrate (e.g., from one surface substantially to another opposing surface). The via may be used to accommodate electrical connection of a semiconductor device, an electrical component, or circuitry located on a side of the substrate other than where bond pads have been formed. Vias are conventionally formed in a variety of substrates for a variety of uses. For example, interposers for single die packages, interconnects for multi-die packages, and contact probe cards for temporarily connecting semiconductor dice to a test apparatus often employ vias in their structures.
In a more specific example, a test apparatus may be configured for the temporary and simultaneous connection of bond pads of a semiconductor die (e.g., on a full or partial wafer test apparatus). A substrate, employed as a test interposer, may include vias passing therethrough providing a pattern of conductive interconnect structures on one side of the interposer substrate to match the bond pad patterns of the semiconductor dice, as well as a plurality of interconnect structures on an opposing side of the interposer substrate for connection with the test apparatus. Thus, the vias of the interposer substrate provide electrical interconnection between the semiconductor dice (or other device) and the test apparatus.
Where a via is to be formed through a semiconductive material such as silicon, one known method for constructing the via includes forming a first hole (sometimes referred to as a “precursor hole”) by a so-called “trepan” process, wherein a very small bit of a router or drill is rotated about a longitudinal axis while being moved radially about the axis to create the precursor hole. The precursor hole is larger in diameter than the intended diameter of the completed via. Following precursor hole formation, an insulation (or dielectric) layer is formed in the hole by either forming a thin silicon oxide layer on the hole's surface by exposure to an oxidizing atmosphere or by oxidizing the hole and then coating it with an insulative polymeric material. When a polymeric insulative material coating is desired, a suitable polymer, such as PARYLENE™ polymer, may be vapor deposited over the substrate and into each precursor hole on one side thereof while applying a negative pressure (i.e., a vacuum) to an opposing end of the hole. In some cases, because adhesion of a given polymer material to the silicon may be relatively poor, the surface of the hole may be oxidized to improve adhesion of the polymer material.
The insulative polymeric material is drawn into and fills each precursor hole and the polymer is cured. A via hole is drilled (such as by percussion drill or laser) or otherwise formed in the hardened insulative polymeric material so as to exhibit a diameter smaller than that of the precursor hole. The via hole is then filled with a conductive material, which conventionally includes a metal, metal alloy, or metal-containing material, to provide a conductive path between the opposing surfaces of the substrate. The conductive material of the via is insulated from the substrate itself by the layer or layers of insulative polymeric material.
While such a method provides adequate structures for enabling electrical interconnection from one surface of a substrate to another surface of the substrate, it is noted that it is difficult to achieve dense spacing of vias and difficult to form vias exhibiting high aspect ratios (i.e., height to width, or cross-sectional dimension ratios) using such a method.
In another prior art method of forming a via, a silicon wafer is provided with a thin layer of silicon dioxide on both major, opposing surfaces. A pattern is formed on the wafer by use of mask layers which prevent etching in non-via areas. An etchant is applied to both major surfaces to form holes or “feedthroughs” which meet in the middle of the wafer. A dielectric layer is then formed over the wafer surfaces including the feedthrough side walls. A metal layer is formed over the dielectric layer and conductive material is placed in the feedthroughs to complete the conductive vias. It is noted that, in order to isolate each via, the metal layer must be configured to cover the feedthrough surfaces only, or be subsequently removed from the outer surfaces of the via and wafer. Again, it is difficult to obtain high aspect ratio vias using such conventional methods and, therefore, provide a high level of density of such vias for a given application.
Other prior art methods for forming vias are generally illustrated in U.S. Pat. No. 5,166,097 to Tanielian, U.S. Pat. No. 5,063,177 to Geller et al., and U.S. Pat. No. 6,400,172 to Akram et al.
It is a continuing desire to improve the manufacturing techniques and processes used in semiconductor fabrication. It would be advantageous to provide a more efficient method for forming through-wafer interconnects that enables a higher density of vias, enables the fabrication of high aspect ratio TWI structures and improves the simplicity of the fabrication process while maintaining or improving the reliability of the TWI structures.